The present invention relates to axle mechanisms, and, more particularly, to a "universal" axle lubrication system. As used herein, the term universal will be understood to mean a lubrication system which operates effectively for each of four modes of operation of the axle mechanism, to be designated hereinafter as follows:
Rf -- right-Side-Up, Forward PA1 Rr -- right-Side-Up, Reverse PA1 Uf -- upside-Down, Forward PA1 Ur -- upside-Down, Reverse
The invention is particularly applicable to axle mechanisms of the type employed in relatively heavy vehicles, such as on-highway and off-highway trucks, tractors, buses, etc., and will be described with reference thereto. However, it will be appreciated that the invention may have broader application and may be applied to axle mechanisms in other types of vehicles, as well as to other motion transmitting axle mechanisms.
Axle mechanisms of the type which the present invention relates typically include a housing, generally comprising a differential carrier housing and an axle housing. Disposed within the differential carrier housing is a drive pinion shaft, a pinion gear mounted on the shaft, a ring gear in meshing engagement with the pinion gear, an axle differential mounted for rotation with the ring gear, and a pair of axle shafts. In such axle mechanisms, the primary objective of the lubrication system, and of the present invention, is effective lubrication of the differential unit. When the opposite axle shafts are rotating at substantially the same speed, and in the same direction, all of the parts of the differential unit rotate substantially as a single entity, and with little or no relative movement between the parts of the differential unit, there is less concern about lubrication of the unit. However, during a "spin-out" condition, or any other condition resulting in unequal speed of the opposite axle shafts, there is relative movement between the various parts of the differential, e.g., the differential, e.g., the differential pinions and pinion shafts rotate within the differential housing, the pinions are in driving engagement with the differential side gears, and the thrust washers are loaded.
Although a spin-out condition frequently occurs for only a few seconds, such as when one of the driven wheels skids on a slippery spot on the driving surface, it also commonly occurs that a spin-out condition will be encountered over a longer period of time. Typically, this happens as the vehicle is progressing up a long grade and one of the driven wheels maintains engagement with the driving surface while the other is spinning or slipping. It will be appreciated that in this situation, if insufficient lubrication is fed to the differential unit while the parts of the differential are subjected to extreme speed differences over a long period of time, a failure is likely to occur.
Prior art axle mechanisms have utilized a number of different arrangements for lubricating the axle differential unit. For example, it has been well-known in the art to utilize openings or "windows" in the differential case, such that rotation of the case through the lubricant in the sump would permit the lubricant to enter the differential case through the windows. However, such an arrangement has been found to be generally unsatisfactory as somewhat of a "hit-or-miss" proposition, i.e., not sufficiently positive and certain to provide lubrication to all of the wear points within the differential unit.
Another common arrangement has utilized a rubber scraper or pick-up director member, typically attached to a portion of the differential carrier housing, and disposed to scrape or wipe lubricant from the O.D. of the differential case as the case rotates, passing through the sump and picking up lubricant thereon. The lubricant thus picked up by the pick-up-director member is then directed into a passageway, from where it flows into the differential unit, in the regions in which it is most needed. The use of such a pick-up-director member has been fairly common and generally satisfactory, but each such member usually functions only in one of the four operating modes of the axle mechanism. Thus, with only one such director member present, the axle mechanism is limited to one mode of use (i.e., RF, RR, UF, or UR).
In addition to limiting the modes of operation of the axle mechanism, the use of the pick-up-director members has other disadvantages. One is the manufacturing cost, as each such member represents the addition of one molded, rubber part having no other function, as well as fasteners required, typically several small bolts which necessitate a separate drilling and tapping operation on the differential housing. In operation, the pick-up-director members have been less than satisfactory for two main reasons; first, when the differential case is rotating in a direction opposite to that intended for use with the director member, the member has a tendency to engage the outer surface of the differential case and become rolled under, possibly damaging the scraper. Secondly, it should be understood that the amount of lubricant picked up on the scraper is a function of the film thickness, i.e., the thickness of the film of lubricant on the O.D. of the differential case after it passes through the sump. The film thickness is, in turn, dependent upon the temperature of the lubricant, the viscosity and film thickness of the lubricant on the differential case being greatest at ambient temperatures, while at operating temperatures (typically 180.degree. to 220.degree. F.), the lubricant has a lower viscosity and decreased film thickness.
Another approach to the problem, although still utilizing a pick-up-director member, is illustrated in U.S. Pat. No. 3,838,751, assigned to the Assignee of the present invention and incorporated herein by reference. In the lubrication system of the cited patent, a pick-up-director member is used, either directly or indirectly, to feed lubricant to the differential unit in both the RF and RR conditions, while in the UF and UR modes, the pinion gear rotating through the sump is utilized to direct lubricant to the differential. It was found, however, that the configuration of the differential carrier housing in the cited patent made manufacture thereof difficult, especially with regard to the necessary support for the various cores during the casting process.